This section provides background information related to the present disclosure which is not necessarily prior art.
Engines that operate on dual fuels are common in the marine industry where various emission regulations may be in effect in coastal areas, but not in effect while out to sea at a predetermined distance from land. For example, the engine on a marine vessel may operate using a lower-sulfur-containing fuel while close to shore, and operate using a high-sulfur-containing fuel while out at sea.
Combustion of sulfur-containing fuels produces exhaust including sulfur. The sulfur in the exhaust can increase production of sulfur oxides (SOX) that may be detrimental to the environment. Further, the sulfur in the exhaust can react with exhaust after-treatment reagents to produce by-products such as ammonia bi-sulfate. After prolonged periods of exposure to ammonia bi-sulfates, catalyst-coated substrates of an exhaust after-treatment system can become plugged, which reduces the efficacy of the exhaust after-treatment system.
Some fuels are more apt to producing ammonia bi-sulfates, including fuels having a higher sulfur content. To address these concerns, fuel suppliers have developed lower sulfur content fuels. Fuels having lower sulfur content, however, are more expensive due to the increased costs in production of the fuels. In view of these fuel costs, the above-noted dual fuel engines have been developed. During a fuel switch, however, it is not uncommon for residual fuel to remain in the exhaust system. If the fuel in the exhaust system has a higher sulfur content, the residual fuel can produce greater amounts of ammonia bi-sulfate that can, over prolonged periods, plug the catalyst-coated substrates of the exhaust after-treatment system.